1. Field of the Invention
The present invention provides a method for the production of isocyanates. In particular, the invention provides a method for the production of an isocyanate, R (NCO).sub.x, by catalytically cracking at elevated temperature an amide having the formula ##STR2## wherein R is an alkyl or aryl group having 1 to 20 carbon atoms, x is 1 to 3, and R.sub.1 is an alkyl group having 1 to 4 carbon atoms.
2. Description of the Prior Art
Isocyanates are chemicals of great commercial importance, finding widespread use in the formation of urethanes and polyurethanes, for example. Procedures primarily used in the production of isocyanates involve the reaction of phosgene with the corresponding amine to form the isocyanate. Toluene diisocyanate which is widely used in the preparation of polyurethanes is made commercially by the reaction of toluene diamine with phosgene.
Because of the problems and expense associated with the use of phosgene, workers in this art have long sought alternative processes for isocyanate production. See, for example, such comprehensive reviews as "Syntheses and Preparative Applications of Isocyanates" by Reinhard Richter and Henri Alrich, Chapter 17, p. 619 of "The Chemistry of Cyanates and Their Thio Derivatives, Part 2," editor Saul Patai, published by John Wiley and Sons, 1977, New York, an Interscience Publication.
U.S. Pat. No. 3,314,754 shows the production of isocyanic acid by pyrolysis of alkyl carbamates.
Mukaiyama, et al. in Journal of the Chemical Society of Japan, Vol. 36, pages 95 through 99 (1963), showed the formation of small amounts of isocyanates by pyrolysis of phenylacetanilide.
Despite the efforts of prior workers to develop alternate routes to isocyanates, the phosgene process remains as the dominant commercial process.